1. Field of the Invention:
This invention relates to a brake operating system, and more particularly to a novel and improved brake operating system for use in electrically driven vehicles.
2. Description of the Prior Art:
In general, electrically driven vehicles, especially large-sized electrically driven construction vehicles, of which driving wheels thereof are rotatably driven by an electric motor include a pneumatically operated brake, which is hereinafter called as a pneumatic brake, and an electric brake in which a braking energy is converted into an electric energy by utilizing the electric motor as a generator when the braking operation is acted on the vehicles.
In many of conventional brake operating systems for use in such electrically driven vehicles, both the pneumatic brake and the electric brake are operated through their respective brake valves by the action of compressed air when a brake pedal is depressed. The compressed air is supplied through a pneumatic circuit from an air compressor into main and sub air storage tanks connected to each other by the interposition of a check valve and further supplied therefrom through the respective brake valves into a pneumatic circuit for the pneumatic brake and that for the electric brake, respectively, so as to operate those brakes. Therefore, if any trouble should happen in the pneumatic circuit provided between the compressor and the main tank, the supply of compressed air not only to the main tank but also to the sub tank will be stopped. As a result, it becomes impossible to apply not only the pneumatic brake but also the electric brake to a vehicle. In addition, in the conventional system, it has not been possible to make brakes for front and rear wheels of the vehicle independent of each other because the pair of brake valves of a dual treadle type are provided for the pneumatic and electric brakes so as to divide the respective circuit into two lines independent of each other.
The brake valves should be preferably provided in the pneumatic circuit for the pneumatic brake so as to divide the circuit into two lines which are independent of each other and respectively connected to the respective brakes for the front and rear wheels, thus either of the respective brakes for the front and rear wheels may perform the braking function even if any trouble should happen in either of the two lines.